口腔碘泡虫宿主新纪录及种群分化研究

New Host Record of Myxobolus oralis and Its Population Differentiation

【目的】研究口腔碘泡虫(Myxobolus oralis)宿主新记录及种群分化。【方法】基于形态特征、18S r DNA序列相似度、遗传距离、变异位点、系统发育以及18S rRNA序列V4区二级结构的预测,对口腔碘泡虫江西种群和湖北种群进行了比较分析。【结果】口腔碘泡虫江西种群与湖北种群形态学特征基本一致;两种群18S r DNA序列相似度为99%,变异位点数为6个,遗传距离为0.003,18S rRNA序列V4区二级结构无差异;口腔碘泡虫湖北种群先于江西种群分化出来。【结论】口腔碘泡虫与宿主可能并未经历协同进化的自然历史过程;口腔碘泡虫可能先寄生于异育银鲫(Carassius auratus gibelio),然后少数个体偶然发生宿主转移事件而进入鲫(Carassius auratus auratus)体内并在长期的进化中逐渐适应这种新的寄生关系,最终形成新的种群或亚种。

[Purposes]It is aimed to investigate the new host record of Myxobolus oralisand its population differentiation. [Methods]Comparative analyses were conducted on M. oralis from Jiangxi population and Hubei population based on their morphological characteristics,18 S r DNA similarities,genetic distances,sequence variation,phylogenetic analysis and V4 region of secondary structure of 18 S rRNA. [Findings]Basically,the populations of M. oralis from Jiangxi and Hubei shared a consistent morphological characteristics; the two populations have 99% similarity on 18 S r DNA sequences,6 sequence-variation sites,0.003 genetic distance,no variation of V4 region based on 18 S rRNA sequences; M. oralis from Hubei population diverged earlier than Jiangxi population. [Conclusions]M. oralis and its host may have not experienced a process of natural co-evolution; M. oralis may parasite on Carassius auratus gibelio firstly,and then（ since the very similar diets and habitats of C. auratus auratus and C. auratus gibelio,the two kinds of fish are always yielded in polyculture pond） a small number of individuals of M. oralis from C. auratus gibelio migrated to C. auratus auratus,and with the evolution process for a long run,the migrated parasites gradually adapted to the new parasitic relations,and then they finally became a new population（ or subspecies） on a new host.